feat(gpu): refactor the sample extract entry point

[pdroalves]

feat(gpu): refactor the sample extract entry point so the user can pass how many LWEs should be extracted per GLWE

closes: https://github.com/zama-ai/tfhe-rs-internal/issues/925

PR content/description

Check-list:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• Relevant issues are marked as resolved/closed, related issues are linked in the description
• Check for breaking changes (including serialization changes) and add them to commit message following the conventional commit specification

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[guillermo-oyarzun]

why is this hardcoded to 2?

[pdroalves]

No particular reason. I just wanted to test for some value different than lwe_per_glwe = polynomial_size, since this case is already covered with compression.

Do you think it should be something else?